Hi,
Welcome to HCM,
Your mother is diabetic and Overweight, actually diabetes is more common in obesity due to insulin resistance and which could be a part of Metabolic syndrome.
If she is overweight and her knees are also not healthy still she should be encouraged to have some physical activity.
She should be seen by internal medicine specialist /Endocrinologist and proper examination with height and weight and calculating BMI,along with blood pressure and Lipid profile and cardiac status by EKG.
If her blood sugar is borderline then she can be controlled by diet and regular exercise,diet is 25 K cal/body weight you can take help of Dietitian avoiding refined sugar and food with high glycemic index like potato.Fats and fried items and animal fats.
Increased hunger and thirst are signs of Diabetes and she needs to take small and at lease 3 to 5 meals per day as permitted by diet chart.
Physical activity of walking briskly at least 30 to 45 min daily.
If her diabetes is under control continue it if required take prescription drugs.
Please take care
Good Luck

Hi
Diabetes mellitus is a group of metabolic diseases in which the person has high blood sugar due to either pancreas didn't secret enough amount of insulin to control the blood sugar or the cells fail to respond the insulin in the blood.
Symptoms are excessive thirst, excessive hunger and frequent urination.
As your mom is obese her Diabetes cannot be controlled only in diet without exercise and medication so consult diabetologist to check her blood sugar for the past 12 weeks the test called glycosulated hemoglobin HbA1c and other blood investigations to rule out the other endocrine disorder. After completely investigation procedure if she follows correct diet, regular yoga practices to control her blood sugar, over weight, to avoid stress and proper medications definitely she can lead a healthy life by keeping her sugar level under control and by preventing the complications due to uncontrolled diabetes. Follow these suggestions also
Drink plenty of water
Chew the food properly before swallow because salivary juice helps in the process of digestion and gives the person full satisfaction of eating even if she consumes less food.
S
Always have 1/2 a stomach of food 1/4water and1/4 air.
Have lots of fiber rich foods prevents the excess absorption of sugar front the intestine.
Add lots of green leafy veg and vegetables in diet
Avoid oily spicy food, junk foods , sweets, excess intake of non veg, fried items, coconut, groundnuts
Avoid stress.
Hope I answered your query.
Take care.
Bye